1. Field of the Invention
This invention relates to refrigeration units which cool air by drawing it over finned coils through which a refrigerant is flowing, and in particular, to a refrigeration unit incorporating a hot gas defrost circuit including an anti-bridging circuit.
2. Description of Related Art
Air cooling units are widely used to cool a variety of storage and working spaces, such as storage areas for produce, meat and frozen goods. In general, air cooling units comprise a finned coil assembly through which a refrigerant is directed, an electrically driven fan for drawing or pushing air through the finned coils, and a condensate collection pan fitted below the finned coil assembly to collect and divert water condensed from the air as it passes over the coils and is cooled below its dew point. The condensate pan is fitted with a drain through which the condensate is directed to the building drain system as appropriate. A compressor and condenser assemblies are also required for providing refrigerant to the cooling coils. The compressor and condenser assemblies are usually provided as separate units, and may be located remotely from the air cooling unit.
During normal operation, it is common for condensate collecting on the coils and in the condensate pan to periodically freeze. Therefore, air cooling units are usually fitted with a defrost mechanism, which is usually located in the condensate pan directly below the lower end of the cooling coil assembly. The defrost unit may either be an electrical resistance heater, or may consist of a separate coil assembly for receiving hot refrigerant gas from the outlet of the refrigeration compressor. The defrost mechanism may be activated periodically at predetermined intervals, or may be activated in response to a buildup of frost detected either visually or by other means. In spite of the presence of either electric or hot gas defrosters however, the area between the front edge of the condensate pan and the lower front edge of the cooling coil assembly can be the plagued by a buildup of ice which is not adequately alleviated by known defrosting mechanisms. Once a buildup of frozen condensate occurs in this area, freezing of the condensate in the condensate pan is more frequent, requiring more frequent defrost cycles, or perhaps resulting in overflow of condensate onto the floor below, causing a slipping hazard and maintenance problem.
As a result, there remains a need for an improved refrigeration cooling unit defroster which in addition to defrosting the cooling coils and a major portion of the condensate pan, further insures effective defrosting of the area between the lower front edge of the cooling coil assembly, the condensate pan and its drain.